Oracle Function vs. HANA Table Function

Hi,

When migrate Oracle to Hana,we create some table functions to replace oracle's.But how can I get the same result in hana like in oracle.

--Oracle syntax,GetUserNames() is the function name.

SELECT

    MailID

    ,AuthorID

    ,ReceiverID

    ,GetUserNames(ReceiverID) Receiver

FROM

    AllMails

WHERE FetchTime is null

--HANA,create the same table function GetUserNames(),but it's can be only placed in from clause,How can I the get the same result as within an single SQL except call the function in another procedure.

Thanks.

Kelvin